Of the schools that did exceptionally well in the 2005 A-level results, three in Wales stood out. They are all small to medium-sized schools in rural or mixed urban and rural areas with small sixth forms, and were ranked in the top 250 of 3,600 comprehensives in England and Wales by a national newspaper.
What were the factors that enabled Llanidloes high, in Powys, to come 26th out of around 3,600? Was Builth Wells high school's achievement (36th) a one-off phenomenon? Were there features of teaching and learning at Ysgol Gyfun Ddwyieithog y Preseli (137th) which enabled it to add value beyond that expected?
I interviewed the three headteachers to find out how they accounted for their success. All three schools draw on a cross section of working-class and middle-class backgrounds, with a small but growing proportion of students drawn from further afield as their reputation for higher educational standards has grown.
In each case, the school is at the centre of the community and known for initiating innovative cultural and sporting activities. Whatever their strategies, plans and policies, what the schools have in common is that these are owned and supported by all staff as well as managers.
First, each school has generated a climate of high expectation. The students know they should be aiming high and are given a belief in their abilities and the means to reach their targets.
Even where students have been underachieving, particularly boys, there is a belief that there is time for them to catch up and develop in the sixth form.
The schools provide an induction period for the sixth form, with individual advice and guidance drawing on the schools' earlier knowledge of pupils and their strengths. Moreover, each school endeavours to provide a range of subjects to help motivate and inspire them.
Each school monitors the progress of individuals and gives regular feedback. Coasting is not an option. For example, one school sets half-term examinations, followed by interviews with those who have fallen below their target grades.
Another ensures students are given not only grades for coursework and homework, but also advice on how to maintain and improve their work. These practices lead students to work consistently throughout the sixth form.
They learn more effectively, mastering smaller chunks of knowledge at a time and ironing out problems well before external examinations. The judicious use of assessment improves learning and encourages young people to do better.
The quality of teaching is key, and professional development is prioritised. Sixth-form teaching is generally delivered by a mixture of experienced and relatively new teachers.
Teachers are willing to go the extra mile, including extra tuition in lunch breaks and after school. They use a variety of teaching methods, taking into account the different ways students learn (for example, visual, auditory and kinaesthetic).
The schools all have strategies for study skills, homework, coursework and revision. There are whole-school and departmental instruments such as a sixth-form planner, which includes pastoral details, tutor information and the school email addresses of staff so students can contact them easily where needed.
One school provides detailed guidelines on coursework. All this helps the students to plan and work effectively, making the best use of their time.
Examination performance is profoundly influenced by partnerships between the various groups involved in the students' success - heads, senior management, teaching staff, students and parents. Students feel supported by teachers and hear criticism as valuable feedback. The relationship with parents is close and co-operative.
Finally, the schools harness the social and cultural expectations of the students, rather than trying to impose expectations. The fact that most sixth-formers work part-time is accepted, and one school encourages students to seek employment in areas which will complement their studies.
The adoption of the Welsh baccalaureate advanced diploma at Builth Wells has proved highly beneficial in helping students to see how much they can fit into their lives while doing A-levels.
The school has gone to great lengths to provide a coherent package across the full range of Welsh bac activities, linking work experience, community and project work.
The bac structure provides a framework within which students can work not necessarily harder but more efficiently. The other two schools have decided to enter all their sixth-formers for the Welsh bac next year.
The high expectations, culture of success and hard work, regularity and constructiveness of feedback through testing and discussion, combined with high-quality teaching, crystallise the aspirations of students and enable them to work harder and more effectively, producing exceptional results.
Alan Evans is a research consultant at Cardiff university's school of social sciences